I've been reworking the wiring in my little Grandt Line GE 23-tonner. It has a NCE N12SRP and has been a relatively strong performer considering its dimunitive size. It managed to blow its headlight LEDs after a wayward wire got snagged by the geartrain.
Since I had a TCS KA-1 sitting around I figured I'd see if I could fit it in. Just barely physically. I connected the blue and white stripped wire to the blue wire and probed for a negative connection to solder the back and white striped wire to. Found a brass hole next to the main chip that seemed to test correctly so connected to it.
Now I have Keep Alive in Reverse only. The Reverse headlight stays on after lifting from the track. However, while there seemed to be some Keep Alive in Forward, I think my eyes were deceiving me. Certainly the headlight doesn't stay on like it does in Reverse.
First time this has happened in about half a dozen Keep Alive hacks. If ayone has specific suggestions on the N13SRP or more generic suggestions on what to try next? There are several other open connections available, but they are even more cramped in than the one I used, if viable. Probably I'm on the wrong side of a diode or sumthin'...
Mike Lehman
Urbana, IL
Wait, which decoder is this? NCE doesn't show an N13 or N12SRP. If the layout is like other NCE decoders, they use 4 diodes instead of a bridge, and there appears to always be a capacitor across the + and - sides - these are you connecting points for the stay alive, the + side should also be the blue wire. Once you are next to the main chip, you are probably past the motor drive.
Post some clear close up pics of both sides of the decoder, it will probably be visible.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
the connection for the blue and blue/white wires seems correct ..
the negative connection will be harder to find, but usually on one of the four main diodes coming off the the track power ... it should be on the circuit side, not -directly- tied to track power
rrinker Wait, which decoder is this? NCE doesn't show an N13 or N12SRP. SNIP Once you are next to the main chip, you are probably past the motor drive. Post some clear close up pics of both sides of the decoder, it will probably be visible. --Randy
Wait, which decoder is this? NCE doesn't show an N13 or N12SRP. SNIP
Once you are next to the main chip, you are probably past the motor drive.
I'm pretty sure I matched the right decoder to the pic on the old style NCE info sheet, as I only have a few decoders with only 2 Function outputs. Decoder is too small to have a visible model # on it. It is a discontinued model # and was originally covered in clear shrink.
I suspect you're right I'm too far past the motor drive, except it does have Keep Alive on the motor in reverse.
Pic 1 is the general situation. Pic 2 is cruddy, but I think it gives an idea where the wires go right now. Pic 3 is pretty clear about showing the possible connections vs where I'm hooked up now with the Negative wire on the Keep Alive which the arrow points to.
That capacitor where the decoder's blue wire is, and you soldered the blue from the keep alive? The other side of it should be your negative common for the keep alive. That matches with NCE's design on their larger decoders which plop that cap in the middle of the diodes.
Randy,
Thanks! Yes, soldering to the other side of that cap where I had the blue striped wire did the trick. Keep-Alive is good both directions now. Yippee! Going to put a tiny dot of epoxy on things to hold them solid, then stuff everything into the cab...
Sometimes there is a benefit when there's only one engineer who designs everything - as long as they are consistent. I should have said "most likely" since it was 100% clear with the other wires in the way, but I was pretty confident that was the right place - at least 85% you weren't going to blow up the decoder
That other place you had it connected - that was probably the line going to the rear light, with the full keep alive going to that one LED, it probably would stay on all night.
That makes sense on why it was half-working.
It's also possibkle when I measured the voltage that my test probe may have made contact with one of the closely adjacent legs of thast IC near the brass-ringed hole instead of the brass ring itself. That could have misled me into thinking it was the Negative when it was just the IC "talking." IIt was pretty crowded in there and you're right, when I asked for help it was to try to avoid letting the smoke out. I figured I'd used up my luck last evening getting it running as well as I did and avoiding blowing up the Function outputs when I trashed my lighting.
The LED won't go on all night, but 20 minutes seems about right.